Magnet arrangement

ABSTRACT

In the case of a magnet arrangement for an electromechanical drive with a cylindrical armature guided in a pole tube, the position of the armature is transformed into an electrical signal. Provided for this purpose is a displacement sensor which is connected to the armature and has a fixed part and a movable part. One side of the armature is formed in such a way that it transfers the movement of the armature, the other side of the armature is connected to the movable part of the displacement sensor. The pole tube is provided with a closure part on the side of the displacement sensor. A pressure tube is led to the outside through an axial clearance of the closure part. The movable part of the displacement sensor moves in the pressure tube. The pressure tube is enclosed by the fixed part of the displacement sensor. In order to prevent the displacement sensor from being damaged by vibrations, the fixed part of the displacement sensor is arranged in a clearance of the closure part. Magnet arrangements of this type are preferably used for electrical position feedback in the case of fluidic valves.

[0001] The invention relates to a magnet arrangement for anelectromechanical drive, especially for a fluidic valve, according tothe precharacterizing clause of claim 1.

[0002] A magnet arrangement of this type is known as a component part ofa hydraulic directional control valve from the publication “Neuartige,kostengünstige Antriebe für Proportionalventile in der Fluidtechnik”[novel, low-cost drives for proportional valves in fluid technology],the journal “O+P Ölhydraulik und Pneumatik” [O+P oil hydraulics andpneumatics] 43 (1999) No. 4, pages 252 to 258. Arranged in an axiallydisplaceable manner in the housing of a directional control valve is acontrol piston, which controls the magnitude of the stream of pressuremedium flowing via the directional control valve. In axial extension ofthe control piston, a pole tube is respectively screwed into the housingfrom each of both sides. Pushed over each pole tube is a coil. Guided ineach of the two pole tubes is a cylindrical armature, which exerts aforce deflecting the control piston when current is applied to the coilenclosing it. Connected to one of the armatures is a displacementsensor, which transforms the position of the armature into an electricaloutput signal, which is a measure of the position of the armature. Sincethe control piston of the directional control valve is non-positivelycoupled to the armature, the electrical output signal of thedisplacement sensor is also a measure of the position of the controlpiston. The displacement sensor has a fixed part in the form of a coilarrangement and a movable part, the core. The core is held on a coresupport, which is held on the armature on the side remote from thecontrol piston. The pole tube is closed off on the side of thedisplacement sensor by a closure part, which is provided with an axialclearance. Through this clearance, a pressure tube is led out of thepole tube to the outside. The closure part and the pressure tube ledthrough the latter close off the armature space from the outside in apressure-tight manner. The part of the pressure tube protruding beyondthe closure part in the axial direction is concentrically enclosed by acoil arrangement, which forms the fixed part of the displacement sensor.The coil arrangement is arranged in a housing of its own. This housingis held on the pole tube by a clamping clip, which engages in an outerannular groove of the closure part. Additionally provided is aserration, which prevents the housing from turning with respect to thepole tube. The core of the displacement sensor moves in the region ofthe pressure tube enclosed by the coil arrangement. The housing of thefixed part of the displacement sensor bears against the coil and securesthe coil in the axial direction. This type of fixing of the coil is morecomplex than the fixing of the coil by a nut which engages in anexternal thread on the closure part, as is customary in the case of apole tube without a displacement sensor, and increases the number ofdifferent parts. The arrangement of the displacement sensor in axialextension of the pole tube makes the directional control valve providedwith the displacement sensor susceptible to vibrations, which in anextreme case may lead to the displacement sensor being torn off.

[0003] The invention is based on the object of providing a magnetarrangement of the type stated at the beginning in which the risk ofdamage caused by vibrations is significantly reduced.

[0004] This object is achieved by the feature characterized in claim 1.Since the entire displacement sensor is arranged inside the closure partof the pole tube, a very compact construction of the magnet arrangement,in which the displacement sensor is also protected from mechanicaldamage, is obtained. A separate housing is not required for the fixedpart of the displacement sensor. Moreover, there is no longer any needfor measures for fastening such a housing on the pole tube. The closureparts containing the fixed part of the displacement sensor can beproduced and tested on their own.

[0005] Advantageous developments of the invention are characterized inthe subclaims. They comprise structural design details of the magnetarrangement, in particular those which allow a simple arrangement of theelectronic components of a circuit arrangement for evaluating the outputsignals of the displacement sensor and also a simple connection ofexternal electrical lines. The subclaims also comprise structural designmeasures which concern the configuration of the closure part of the poletube.

[0006] The invention is explained below more precisely with its furtherdetails on the basis of exemplary embodiments represented in thedrawings, in which:

[0007]FIG. 1 shows a section through a magnet arrangement formedaccording to the invention,

[0008]FIG. 2 shows the region of the closure part of the magnetarrangement represented in FIG. 1 in an enlarged representation,

[0009]FIG. 3 shows a section through a further closure part with aterminating part for a magnet arrangement according to the invention,

[0010]FIG. 4 shows a section through a third closure part with aterminating part for a magnet arrangement according to the invention,

[0011]FIG. 5 shows a section through the terminating part represented inFIG. 4,

[0012]FIG. 6 shows a section through a fourth closure part for a magnetarrangement according to the invention and

[0013]FIG. 7 shows a section through a further closure part with aterminating part, the closure part and the terminating part beingconnected to each other by means of a screw drive.

[0014] The same components are provided in the figures with the samedesignations.

[0015]FIG. 1 shows a section through a magnet arrangement 10 with a poletube 11, an armature 12 guided in the pole tube 11 and a closure part13. The pole tube 11 is screwed into a housing 14 of a fluidic valve,only represented schematically. Formed onto the armature 12 on the sidefacing the housing 14 is a tappet 15, which deflects a control piston(not represented here) of the valve. An only schematically representedmagnetic coil 16 encloses the pole tube 11. The magnetic coil 16 is heldbetween the housing 14 and a nut 17, which engages in an external thread18 of the closure part 13. Arranged between the armature 12 and theclosure part 13 is a spring 19. The spring 19 ensures a defined positionof the armature 12 when the magnetic coil 16 is not energized. Thespring 19 is no longer needed if a defined position of the armature 12with the magnetic coil 16 deenergized is ensured in some other way. Ifthe magnetic coil 16 is energized, the armature 12 is correspondinglydeflected. Arranged on the side of the armature 12 facing the closurepart 13 is a core holder 21, provided with a core 20. The core 20 formsthe movable part of a displacement sensor. The displacement sensortransforms the position of the armature 12 into an electrical signal,which is a measure of the position of the armature 12. The closure part13 is provided with a clearance 24, which is sealed by a terminatingpart 25. Details of the connection of the terminating part 25 to theclosure part 13 are not specifically represented. The two parts may, forexample, be adhesively bonded to each other. Integrated into the endface of the terminating part 25 is a connector 26. The terminating part25 is provided with a clearance 27, which goes over into the clearance24 of the closure part 13. A coil arrangement, comprising two secondarycoils 28 a and 28 b and also a primary coil 28 c surrounding the latter,forms together with a support 36 the fixed part of the displacementsensor. The support 36 with the coils 28 a, 28 b and 28 c is arranged inthe clearance 24 of the closure part 13. The coils 28 a and 28 b as wellas 28 c are arranged concentrically in relation to the core 20. Furtherdetails of the displacement sensor are described on the basis of FIG. 2.

[0016]FIG. 2 shows a detail from the magnet arrangement 10 representedin FIG. 1, in an enlarged representation. Components which have alreadybeen described above are not described again in connection with FIG. 2.A pressure tube 29, which is closed at one end and is provided at itsopen end with a collar 30, protrudes into the clearance 24 of theclosure part 13. The collar 30 is supported on an annular face 21,facing the armature 12, of the closure part 13. A peripheral weld 32ensures a pressure-tight connection between the collar 30 of thepressure tube 29 and the closure part 13. It is possible to dispensewith the weld 32 if a pressure-tight connection between the collar 30and the closure part 13 is established in some other way. As analternative to this, it is possible to form the closure part and thepressure tube as one piece. The free end of the pole tube 11 is flangedinto a first annular groove 33 of the closure part 13. A sealing ring 34is arranged between the closure part 13 and the pole tube 11 in afurther annular groove 25. In order that the magnetic coil 16 can bepushed onto the pole tube 11, the outside diameter d₁₈ of the externalthread 18 is chosen to be slightly smaller than the outside diameter d₁₁of the pole tube 11. Of the winding ends of the coils 28 a, 28 b and 28c arranged on the support 36, two winding ends are represented,designated by 37 and 38. In the simplest case, the winding ends 37 and38 are connected directly to terminal pins 41, 42 of the connector 26.It is also possible, as schematically represented in FIG. 2, for aprinted circuit board 39, which is loaded with electrical components 44,45 of an electrical evaluation circuit, to be held on the terminal pins41, 42 of the connector 26. In this case, the winding ends 37, 38 areconnected to the input of the evaluation circuit and the output of theevaluation circuit is connected to the terminal pins 41, 42.

[0017]FIG. 3 shows a further closure part 50 with a terminating part 51.As represented in FIGS. 1 and 2—the printed circuit board 39 is held onthe support 36 for the coils 28 a, 28 b and 28 c of the fixed part ofthe displacement sensor. The support 36 has been pushed over a pressuretube 53, which for its part is held on the closure part 50. The pressuretube 53 is provided with a collar 54. The collar 54 is supported on theannular face 31 of the closure part 50. The collar 54 is provided on theside facing the armature 12 with a clearance 55, which is formed as aguide for the spring 19 represented in FIG. 1. The collar 54 isconnected in a pressure-tight manner to the closure part 50 by aperipheral weld 32. The printed circuit board 39 is provided withsoldering points 57 and 58, to which the winding ends 37 and 38 areconnected. An electrical cable 60 is led through the terminating part 51in the axial direction. In the region where it passes through, the cable60 is surrounded by a grommet 61. Formed onto the terminating part 51 asan additional means for preventing kinking is a tubular continuation 62,extending the terminating part 51. The individual lines 63, 64 of thecable 60 are connected to further soldering points 65, 66 of the printedcircuit board 39. In the simplest case, i.e. when no evaluation circuitis provided, the soldering points 57, 58 are connected to the solderingpoints 65, 66. In the exemplary embodiment represented in FIG. 3, theprinted circuit board 39 is connected to an evaluation circuitschematically represented by the electronic components 44, 45, the inputof which is connected to the soldering points 57, 58 and the output ofwhich is connected to the soldering points 65, 66.

[0018]FIG. 4 shows a third closure part 67, in which a terminating partformed as a plate 68 is screwed to the closure part 67. Formed onto theplate 68 is the connector 26 with the terminal pins 41, 42. The printedcircuit board 39 is mechanically held on the terminal pins 41, 42. Asrepresented in FIG. 2, the support 36 is held on the printed circuitboard 39. The unit formed by the plate 68, the terminal pins 41, 42, theprinted circuit board 39 and the support 36 has been pushed over thepressure tube 53. The printed circuit board 39 with the schematicallyrepresented electrical components 44, 45 of an evaluation circuit isarranged in a clearance 70 of the plate 68. The winding ends 37, 38 ofthe coils 28 a, 28 b, 28 c are connected to the input of the evaluationcircuit. The terminal pins 41, 42 of the connector 26 are electricallyconnected to the output of the evaluation circuit. The plate 68 is heldon the closure part 67 by screws distributed over the circumference, twoof which screws 77, 78 can be seen in FIG. 4.

[0019]FIG. 5 shows a section along the line B-B represented in FIG. 4.In this representation, two further screws 79 and 80 in addition to thescrews 77 and 78 can be seen. In this section, two further terminal pins81, 82 and also two further electronic components 84, 85 can also beseen.

[0020]FIG. 6 shows a further closure part 87. The production of theterminating part of the closure part 87 takes place—as describedbelow—by encapsulating with plastic. The pressure tube 53 protrudes intothe clearance 24 of the closure part 87 and is connected to it in apressure-tight manner. The support 36 with the coils 28 a, 28 b, 28 chas been pushed over the pressure tube 53. The printed circuit board 39is held on the support 36. The terminal pins 41, 42 are mechanicallyheld on the printed circuit board 39. This formation is inserted into anonly schematically represented multi-part mold, which comprises a baseplate 90, two mold halves 91 a, 91 b and an insert 92. Together with theinsert 92, the mold halves 91 a, 91 b enclose a space 24, whichdetermines the later shape of the terminating part and of the connectorformed onto the latter. The mold halves 91 a, 91 b are divided along aplane running through the center axis of the closure part 87, in such away that demolding of the closure part provided with the terminatingpart and the connector is possible. During encapsulation, the space 94and the clearance 24 are filled with liquid plastic via an onlyschematically represented channel 95. In order that the plasticscompound can distribute itself uniformly in the mold, vent holes areprovided in the customary way in the mold and/or in the closure part 87.They are not represented in FIG. 6. Since the plastic also touches partsof the electrical circuit, it is necessary to use an electricallyinsulating plastic for the terminating part. For demolding the closurepart 87 provided with the terminating part and connector, after theplastics compound has solidified the mold halves 91 a and 91 b arepulled apart laterally and the insert 92 is pulled out upward.

[0021]FIG. 7 shows a closure part 100, to which a terminating part 101is connected by means of a screwed connection. Wherever details whichhave already been described in connection with previous figures arerepresented in FIG. 7, the same designations as in the previous figuresare used hereafter for the corresponding components. The pressure tube29 protrudes into the cylindrically formed clearance 24 of the closurepart 100. It is supported with its collar 30 on the end face, facing thearmature of the magnet arrangement, of the closure part 100. Theclearance 24 of the closure part 100 is provided with an internal thread104, and the terminating part 101 is provided with a correspondingexternal thread 105. The internal thread 104 of the closure part 100 andthe external thread 105 of the terminating part 101 form a screw drive,which transforms a rotational movement of the terminating part 101 withrespect to the closure part 100 into an axial movement between the twoparts. The printed circuit board 39 is held on the terminating part 101.Held on the printed circuit board 39 are the support 36 with the coils28 a, 28 b and 28 c, which form the fixed part of the displacementsensor. The region of the terminating part 101 in which the support 36with the coils 28 a to 28 c is located is arranged inside the clearance24 of the closure part 100. The support 36 concentrically encloses thepressure tube 29. The distance between the pressure tube 29 and thesupport 36 is chosen such that the support 36 can move with slight playwith respect to the pressure tube 29. Screwed onto the external thread105 of the terminating part 101 is a check nut 108, which is providedwith an internal thread 107 and prevents unintentional turning of theterminating part 101 with respect to the closure part 100 during theoperation of the displacement sensor. In order to secure the relativeposition of the terminating part 101 with respect to the closure part100, the check nut 108 is screwed against the closure part 100, itsinternal thread 107 being supported on the external thread 105 of theterminating part 101, and the end face provided with the designation 110being supported on the closure part 100. Formed onto the end remote fromthe closure part 100 of the terminating part 101 is the connector 26with the terminal pins 41, 42. The position of the core 20, which formsthe movable part of the displacement sensor, is represented by dashedlines. The axial distance between the fixed part and the movable part ofthe displacement sensor can be changed by turning the terminating part101 with respect to the closure part 100. The terms “fixed part” and“movable part” of the displacement sensor relate to the operation of thedisplacement sensor in which the armature of the magnet arrangementmoves the core 20 and the support 36 with the coils 28 a to 28 c isarranged fixedly with respect to the valve housing. In order to adjustthe displacement sensor, the core is held in a fixed position inrelation to the valve housing and the terminating part 101 is turnedwith respect to the closure part 100, and consequently with respect tothe valve housing, until the electrical output signal present at theterminal pins 41, 42 has assumed a desired value. This position issecured, as described above, by tightening the check nut 108 againstunintentional turning.

[0022] The configuration of the closure part and terminating partdescribed on the basis of FIG. 7 allows a zero displacement of theelectrical output signal to be performed as and when required bymechanical means. With such a zero displacement it is possible, forexample, to correct production-related tolerances with regard to theaxial position of the fixed part of the displacement sensor. Inaddition, it is also possible, by an axial adjustment of the fixed partof the displacement sensor with respect to the closure part, to changethe range of the electrical output signal, so that, for example, insteadof an output signal which moves between a negative maximum value and apositive maximum value, an electrical output signal which moves betweenzero and a positive maximum value or between zero and a negative maximumvalue is obtained.

[0023] By combining the electrical output signal of the displacementsensor with predeterminable threshold values in the form of electricalsignals, the steady output signal of the displacement sensor can be usedas and when required to generate switching signals which signal thereaching of positions of the control piston of a directional controlvalve determined by the threshold values. The combining of theelectrical signals may take place both outside the closure part andinside the closure part, for example by the arrangement of additionalelectronic components on the printed circuit board 39. The switchingsignals are available in addition to the steady output signal of thedisplacement sensor and can be further processed independently of oneanother in devices for control and/or monitoring.

1. A magnet arrangement for an electromechanical drive, especially for afluidic valve, with a cylindrical armature guided in a pole tube andwith a magnetic coil enclosing the pole tube and with a displacementsensor which transforms the position of the armature into an electricalsignal and has a fixed part and a movable part, in which arrangement oneside of the armature is formed for transferring the movement of thearmature and the other side of the armature is connected to the movablepart of the displacement sensor, the pole tube being provided with aclosure part on the side of the displacement sensor, characterized bythe fact that the fixed part (28 a to 28 c, 36; 28 a to 28 c, 69) of thedisplacement sensor is arranged in a clearance (24) of the closure part(13; 50; 67; 87; 100).
 2. The magnet arrangement as claimed in claim 1,characterized by the fact that a terminating part (25; 51; 68) is heldon the closure part (13; 50; 67; 87; 100).
 3. The magnet arrangement asclaimed in claim 2, characterized by the fact that electrical connectinglines (63, 64) of the displacement sensor are led through theterminating part (51).
 4. The magnet arrangement as claimed in claim 2,characterized by the fact that a connector (26) is integrated into theterminating part (25; 68; 101).
 5. The magnet arrangement as claimed inclaim 3 or claim 4, characterized by the fact that the terminating part(25; 51; 68) is provided with a clearance (27; 70), which goes over intothe clearance (24) of the closure part (13; 50; 67).
 6. The magnetarrangement as claimed in claim 5, characterized by the fact that aprinted circuit board (39) is arranged in the clearance (27; 70) of theterminating part (25; 51; 68; 101).
 7. The magnet arrangement as claimedin claim 6, characterized by the fact that the printed circuit board(39) is held on the terminal pins (41, 42) of the connector (26).
 8. Themagnet arrangement as claimed in one of the preceding claims,characterized by the fact that the movable part (20) of the displacementsensor is guided in a pressure tube (29; 53).
 9. The magnet arrangementas claimed in claim 8, characterized by the fact that the pressure tube(29; 53) is provided with a collar (30; 54), which is supported on anannular face (31), facing the armature (12), of the closure part (13;50; 67; 87; 100).
 10. The magnet arrangement as claimed in claim 9,characterized by the fact that the collar (54) is formed as a guide (55)for a spring (19) arranged between the armature (12) and the closurepart (50; 67; 87).
 11. The magnet arrangement as claimed in one of thepreceding claims, characterized by the fact that the closure part (13;50; 67; 87; 100) is provided with an external thread (18), the outsidediameter (d₁₈) of which is smaller than the outside diameter (d₁₁) ofthe pole tube (11).
 12. The magnet arrangement as claimed in one ofclaims 2 to 11, characterized by the fact that the terminating part ismade of plastic and molded onto the closure part (87).
 13. The magnetarrangement as claimed in one of claims 2 to 11, characterized by thefact that the fixed part (28 a to 28 c, 36) of the displacement sensoris held on the terminating part (101) and in that the terminating part(101) can be set with respect to the closure part (100) in the axialdirection.
 14. The magnet arrangement as claimed in claim 13,characterized by the fact that the terminating part (101) is connectedto the closure part (100) by means of a screw drive (104, 105).
 15. Themagnet arrangement as claimed in claim 14, characterized by the factthat the closure part (100) is provided with an internal thread (104)and the terminating part (101) is provided with an external thread(105).
 16. The magnet arrangement as claimed in one of claims 13 to 15,characterized by the fact that securing means (108) which preventunintentional turning of the terminating part (101) with respect to theclosure part (100) are provided.
 17. The magnet arrangement as claimedin claim 16, characterized by the fact that the terminating part (101)is provided with a check nut (108), the internal thread (107) of whichis supported on the external thread (105) of the terminating part (101)and the end face (110) of which, facing the closure part (100), issupported on the latter.